Síntese e caracterização de um composto VOPO4-DMA

A layered matrix, alpha-VOPO4.2H2O was used as host species to produce a VOPO4.dimethylacetamide intercalation compound. The oxovanadium matrix and the synthesized hybrid were characterized by elemental analysis, infrared spectroscopy, thermogravimetry, X-ray diffractometry and SEM microscopy. The X-ray diffraction patterns show that the VOPO4.dimethylacetamide compound is amorphous, but can be turned lamellar after a solubilization-crystallization process. The SEM micrographs obtained for the VOPO4-dimethylacetamide hybrid matrix show that the microstructure of VOPO4.2H2O is changed after reaction, with a delamination of the oxovanadium matrix.

Anisotropic surface properties of micro/nanostructured a-C:H:F thin films with self-assembly applications

The singular properties of hydrogenated amorphous carbon (a-C:H) thin filmsdeposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD), such as hardness and wear resistance, make it suitable as protective coating with low surface energy for self-assembly applications. In this paper, we designed fluorine-containing a-C:H (a-C:H:F) nanostructured surfaces and we characterized them for self-assembly applications. Sub-micron patterns were generated on silicon through laser lithography while contact angle measurements, nanotribometer, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the surface. a-C:H:F properties on lithographied surfaces such as hydrophobicity and friction were improved with the proper relative quantity of CH4 and CHF3 during deposition, resulting in ultrahydrophobic samples and low friction coefficients. Furthermore, these properties were enhanced along the direction of the lithographypatterns (in-plane anisotropy). Finally, self-assembly properties were tested with silicananoparticles, which were successfully assembled in linear arrays following the generated patterns. Among the main applications, these surfaces could be suitable as particle filter selector and cell colony substrate.

Fotoluminescência e adsorção de CO2 em nanopartículas de CaTiO3 dopadas com lantânio

Ca1-xLa xTiO3 powders were prepared by the polymeric precursor method. X-ray diffraction (XRD), FT-Raman spectroscopy, transmission electron microscopy (TEM), and N2 and CO2 adsorption were used for the microstructural and surface characterization of the powders. Room temperature photoluminescence (PL) was observed in Ca1-xLa xTiO3 amorphous particles. The PL intensity of these powders was found to be dependent on the lanthanum molar concentration.

Decomposição térmica de complexos de Zn e Cd com isomaleonitriladitiolato (imnt)

Thermal decomposition of [Bu4N]2[Zn(imnt)2] and [M(NH3)2(imnt)] complexes with M = Zn and Cd, and imnt = (bis 1,1-dicyanoethylene-2,2 dithiolate) in inert atmosphere was investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). Pyrolysis studies at different temperatures, 300, 400, 500, and 600 ºC, in N2 atmosphere were performed and the products were characterized by X-ray diffraction (XRD), infrared and Raman spectroscopy, and scanning electron microscopy (SEM). The products were identified as sulfide sub-micron particles, along with amorphous carbon. Particle sizes estimated by SEM were ca. 50 nm for the cationic complexes and 500 nm for the neutral complexes.

Síntese e caracterização de nanocompósitos Ni: SiO2 processados na forma de filmes finos

We have produced nanocomposite films of Ni:SiO2 by an alternative polymeric precursor route. Films, with thickness of ~ 1000 nm, were characterized by several techniques including X-ray diffraction, scanning electron microscopy, atomic force microscopy, flame absorption atomic spectrometry, and dc magnetization. Results from the microstructural characterizations indicated that metallic Ni-nanoparticles with average diameter of ~ 3 nm are homogeneously distributed in an amorphous SiO2 matrix. Magnetization measurements revealed a blocking temperature T B ~ 7 K for the most diluted sample and the absence of an exchange bias suggesting that Ni nanoparticles are free from an oxide layer.

Estudo comparativo entre sílica obtida por lixívia ácida da casca de arroz e sílica obtida por tratamento térmico da cinza de casca de arroz

A comparison between silica by acid leaching of rice husk (RH) and silica obtained from thermal treatment of rice husk ash (RHA) is presented. The best leaching results were obtained using 10% hydrochloric acid followed by washing with water. The alternative method, calcination of RHA at 700 ºC for 6 h followed by grinding for 80 min, was more effective. Silica obtained from RH was about 97% amorphous, had a 17.37 µm mean particle size, and a specific surface area of 296 m²/g. On the other hand, for silica obtained from RHA the values were about 95% amorphous material 0.68 µm, and 81 m²/g.

Otimização do banho eletrolítico da liga Fe-W-B resistente à corrosão

A study on optimization of bath parameters for electrodeposition of Fe-W-B alloys from plating baths containing ammonia and citrate is reported. A 2³ full factorial design was successfully employed for experimental design analysis of the results. The corrosion resistance and amorphous character were evaluated. The bath conditions obtained for depositing the alloy with good corrosion resistance were: 0.01 M iron sulfate, 0.10 M sodium tungstate and 0.60 M ammonium citrate. The alloy was deposited at 12% current efficiency. The alloy obtained had Ecorr -0.841 V and Rp 1.463 x 10(4) Ohm cm². The deposit obtained under these conditions had an amorphous character and no microcracks were observed on its surface. Besides this, the bath conditions obtained for depositing the alloy with the highest deposition efficiency were: 0.09 M iron sulfate, 0.30 M sodium tungstate and 0.50 M ammonium citrate. The alloy was deposited at 50% current efficiency, with an average composition of 34 wt% W, 66 wt% Fe and traces of boron. The alloy obtained had Ecorr -0.800 V and Rp 1.895 x 10³ Ohm cm². Electrochemical corrosion tests verified that the Fe-W-B alloy deposited under both conditions had better corrosion resistance than Fe-Mo-B.

Calorimetry of hydrogen desorption from ɑ-Si nanoparticles

The process of hydrogen desorption from amorphous silicon (ɑ-Si) nanoparticles grown by plasmaenhanced chemical vapor deposition (PECVD) has been analyzed by differential scanning calorimetry (DSC), mass spectrometry, and infrared spectroscopy, with the aim of quantifying the energy exchanged. Two exothermic peaks centered at 330 and 410 °C have been detected with energies per H atom of about 50 meV. This value has been compared with the results of theoretical calculations and is found to agree with the dissociation energy of Si-H groups of about 3.25 eV per H atom, provided that the formation energy per dangling bond in ɑ-Si is about 1.15 eV. It is shown that this result is valid for ɑ-Si:H films, too

A plasticidade dos amorfos: fazendo pigmentos brancos com fosfato de alumínio

A new white pigment made out of nano-structured non-crystalline aluminum phosphate was recently launched as an industrial product. Pigment opacifying properties are not intrinsic to aluminum phosphate but they arise as the result of a rare hollow particle nano-structure. This is in turn derived from the core-and-shell structure of amorphous aluminum phosphate precipitated under well-defined conditions. The new pigment is a product of the often neglected chemistry of non-crystalline ionic solids that can probably be a rich source of new successful products. The text describes a short account of the R&D activities, from the initial ideas to the present.

Estudo da influência dos íons K+, Mg2+, SO4(2-) e CO3(2-) na cristalização biomimética de fosfato de cálcio amorfo (ACP) e conversão a fosfato octacálcico (OCP)

The crystallization of hydroxyapatite (HA) in aqueous solution can be described by the mechanism ACP -> OCP -> HA. In this work, it was studied the influence of K+, Mg2+, SO4(2-) and CO3(2-) ions in the formation of ACP and in its conversion to OCP, using biomimetic coatings on metallic substrates of commercially pure titanium (Ti c.p.). The results showed that Mg2+ and CO3(2-) ions favored both the formation of ACP and its conversion to OCP. Differently, K+ and SO4(2-) ions did not influence the formation of ACP and, consequently, interfered in the conversion to OCP.

Estabilidad de la glucosa oxidasa en sistemas amorfos formados por los disacáridos sacarosa, maltosa y trehalosa

Glucose-oxidase (GOD), suffers conformational change during freeze-drying. In order to determine the protection level granted by amorphous matrices (AM) of saccharose, maltose, trehalose and their combinations, the thermal inactivation constants (K D) of GOD trapped in these systems were determined. For its evaluation, GOD samples were balanced at different water activities and heated up to 30, 50 and 70 ºC. The best AM found for GOD stability was saccharose-trehalose (5/10% p/v). The K D values (K D.10-4) at a w = 0.0 were 3 at 30 ºC and 6 at 70 ºC. For non-protected GOD under the same conditions these values were 48 at 30 ºC and 257 at 70 ºC.

Desenvolvimento de sistemas líquido-cristalinos empregando silicone fluido de co-polímero glicol e poliéter funcional siloxano

For the construction of the phase diagrams, the method of the aqueous titration was used. There were prepared 5 ternary diagrams, varying the surfactant and the oil phase. The liquid-crystalline phases were identified by polarized light microscopy. The formulations prepared with silicon glycol copolymer, polyether functional siloxane (PFS) and water (S1) and with diisopropyl adipate, PFS and water (S4) presented liquid-crystalline phases with lamellar arrangement. Moreover, after 15 days in hot oven (37 ºC), the formulations presented hexagonal arrangement, evidencing the influence of the temperature in the organization of the system.

Caracterização de cinza obtida por combustão de casca de arroz em reator de leito fluidizado

The rice husk combustion in a bubbling and atmospheric fluidized bed reactor was investigated. This paper presents the rice husk ash characterization employing the techniques of X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM) among others. After combustion, a rice husk ash containing 93% amorphous silica and <3% unburned char was produced. Methods usually applied to fixed bed considering external sources of energy and high reaction times were employed. Thus, the potential of this type of reactors with respect to speed, continuity and self-sufficiency energy of the process was shown.

Fosfatos de cálcio de interesse biológico: importância como biomateriais, propriedades e métodos de obtenção de recobrimentos

For decades the Hydroxyapatite (HA) was only bioceramic of calcium phosphate system used for bone replacement and regeneration, due to its similarity to the mineral phase of bones and teeth. Because its slow degradation, other calcium phosphate classified as biodegradable started to awaken interest, such as: amorphous calcium phosphate (ACP), octacalcium phosphate (OCP) and tricalcium phosphate (TCP). This work presents the evolution of the use of other calcium phosphates due to their better solubility than the HA, comparing their main physical-chemical and biological properties. Are also presented the main methods used to obtain bioceramic coatings on metal and polymer surfaces.

Properties of silica from rice husk and rice husk ash and their utilization for zeolite y synthesis

This study compared properties of silica (SiO2) from rice husk (RH) and rice husk ash (RHA) extracted by acid- and heat-treatment. The SiO2 from RH was in amorphous phase with nearly 100% purity while that from RHA was in crystalline phase with 97.56% purity. Both extracted SiO2 were used in the synthesis of zeolite NaY but that from RH was better due to the efficiency in product recovery and simplicity of extraction. After the NaY was exchanged to NH4Y and calcined to convert to HY, the product did not carry over the textural properties of the parent NaY and NH4Y.